The present invention relates to liquid level sensing devices, and more particularly to a liquid level float switch.
Liquid level sensing devices are often used to indicate the level of liquid in a vessel or other container and/or to operate flow control devices that control the liquid level. A liquid level regulator device manufactured by Flgyt Company, Sweden, under the tradename, Flgyt ENG-10, utilizes a pair of tear-drop shaped plastic bodies which are weighted according to the specific gravity of the liquid in which they are to be used. The bodies are suspended from electrical cables supported above the vessel containing the liquid. The devices are hung at different heights, corresponding to predetermined maximum and minimum liquid levels. When the container is empty, the cables hang vertically within the vessels. When the liquid rises within the vessel to a level sufficient to submerge the device, the device tilts, actuating an attitude sensitive switch within the housing of the device. The switching action is utilized to actuate a pump controller or other liquid level control device. By using this arrangement, the pump may be activated to fill the container when the liquid level drops to a predetermined minimum level and the pump may be deactivated when the level reaches a predetermined maximum level. These devices do not float in the liquid but are arranged so that their base portions are more buoyant than their neck portions which causes the tilting action of the device when finally submerged. The effect of this arrangement is that the switching action of the device is sluggish, and a positive switching action may not be obtained, particularly when there is a degree of turbulence in the liquid within the vessel.
Another disadvantage of this type of regulator device is that, as the body is being submerged, an intermediate stage is reached where the switching mechanism within the device tends to intermittently open and close several times. This is undesirable as it causes the pump motor to be switched on and off and can, as a consequence, cause damage to the pumping motor. This intermittent switching is aggravated when the device is used in industrial applications in which the liquid within the vessel is turbulent.
Reichensperger U.S. Pat. No. 3,483,341 discloses a floating switch comprising a tethered housing containing a pendulum switch. The attitude of the housing varies with the level of liquid in a well. As the attitude of the housing varies, the pendulum switch tilts downwardly or upwardly opening or closing a pair of switch contacts which, in turn activates or deactivates an immersion motor pump. It appears that the Reichensperger device also suffers from the disadvantage noted above wherein the switch rapidly oscillates between opened and closed states, thereby increasing the possibility of pump damage in turbulent conditions.